Thermal type flow meter

Abstract

In a thermal type flow meter having a temperature compensating bridge circuit, the temperature compensating bridge circuit includes a heating resistor, a temperature compensating resistor and a plurality of resistors each having a fixed resistance. The heating resistor and the temperature compensating resistor are supported by a support member in an air flow passage, and the support member is formed by a material having a small temperature coefficient Δλ of thermal conductivity between -0.06 and 0.06 w/m·k 2 . The absolute value of the output error of the flow meter is reduced as a result of variation of the flow quantity or flow velocity of intake air and the intake air temperature.

What is claimed is: 
     
       1. A thermal type flow meter comprising: a first electric resistor, provided within a fluid to be measured, for detecting a flow quantity of said fluid, and a second electric resistor provided within the fluid, the resistance value of which depends on the measured fluid temperature, whereby temperature compensation corresponding to a variation of the measured fluid temperature is carried out by heating said first electric resistor in accordance with the measured fluid temperature detected by said second electric resistor; wherein, the value δ, determined by the following relationship between the total heat value Qt0 and the value Rh0 of electric resistance of said first electric resistor at a predetermined temperature or reference temperature and the total heat value Qt and the value Rh of electric resistance of said first electric resistor at the measured fluid temperature, is within the range of -0.003 to 0.003 at measured fluid temperatures between -30° C. and 80° C. ##EQU7##   
     
     
       2. A thermal type flow meter comprising: a first electric resistor, provided within a fluid to be measured, for detecting a quantity of flow of said fluid, a second electric resistor provided within the fluid, the resistance value of which depends on the measured fluid temperature, and a support member extending from a member containing an electric conductor connected to an electric circuit, whereby temperature compensation corresponding to variation of the measured fluid temperature is carried out by heating said first electric resistor in accordance with the measured fluid temperature detected by said second electric resistor; wherein, said support member includes a lead and a terminal, and the lead is formed by material of which the temperature coefficient Δλ of thermal conductivity is between -0.06 and 0.06 W/m·K 2 .   
     
     
       3. A thermal type flow meter according to claim 2, wherein said support member is formed by an alloy including as a component one of platinum and palladium. 
     
     
       4. A thermal type flow meter according to claim 2, wherein said support member is formed by one of titanium, tantalum, ziruconium, an alloy including one of them, stainless steel and Cr--Mo steel. 
     
     
       5. A thermal type flow meter according to one of claims 1 to 4, wherein at least one portion of the surface of said support member is coated with an anti-oxidation film. 
     
     
       6. A thermal type flow meter according to claim 5, wherein at least one portion of the surface of said support member is coated with one of platinum, platinum alloy, palladium and palladium alloy. 
     
     
       7. A thermal type flow meter according to claim 1, wherein said value of δ indicates a negative inclination with respect to the variation of the measured fluid temperature.